The paint operations of typical automotive assembly plants produce hundreds of thousands of pounds of paint waste annually. Paint that misses the vehicle bodies is collected in the spray booths in a water scrubber. Polymeric materials are generally added to the water which cause the paint to coagulate into particles. After the particles settle, this paint sludge is transported to landfills. In view of the substantial amount of paint waste produced annually, it would be economically and environmentally desirable to extract useful materials from the paint sludge in order to reduce or eliminate the amount of paint sludge that is deposited in landfills.
Attempts have been made to recover useful materials from paint sludge. Kim et al describe a process for pyrolyzing paint sludge mixed with potassium hydroxide at 600.degree. C. to prepare activated carbon. (Paper No. AC945105, 67th Annual Conference of Water Environment Federation, Chicago, Ill. Oct. 15, 1994) This activated carbon is a high surface-area char containing inorganic oxides which is suggested to be useful to trap volatile organic compounds in manufacturing plants. In particular, Kim et al. suggest adding the char into the paint booth scrubber water to remove volatile organic compounds from the spray booth air. This pyrolysis process for converting the paint sludge to char recovers less than 30-40% of the total mass of the dried paint waste. Another approach for paint sludge reclamation is described by Agarwal in U.S. Pat. Nos. 5,129,995 and 5,198,018. They disclose a process and apparatus for the continuous pyrolyric decomposition of waste stream materials containing organic and inorganic components. The inorganic components are recovered, carbon free, and recycled into essentially the same source materials from which they originated. The organic components are collected in liquid or gaseous form, as pyro oil and pyro gas, respectively. They disclose using these organics to fire the apparatus or mixing them with other oil, e.g., heating oil. Hence, the organics are expected to be merely burnt. Argawal's focus is thus on the recycling of inorganic oxides. In the latter patent, for example, dried paint sludge, which comprises about 40% non-aqueous content, is pyrolyzed and about 25% of the non-aqueous content is recovered as inorganic oxide material which is reused as paint filler.
It would be desirable to convert substantially all of the dried paint waste into useful, recyclable materials. The present invention method overcomes the deficiencies of prior paint waste recovery processes in that it typically recovers 100% of the paint sludge as recyclable materials in the form of gaseous materials, volatile liquid materials, and ceramic composite materials, or materials made therefrom.